A first conventional fixing means (1) for a connecting portion between the torch base and the torch head is a cap nut type threading structure as disclosed in the Japanese Examined Patent Publication No. Heisei 3-27309 and Japanese Examined Patent Publication No. Heisei 5-5589.
A second conventional fixing means (2) is the combination of a claw shaped projecting portion which is provided on one of the torch head and the torch base and inclined projection which is provided on the other of the torch head and the torch base so as to establish thread-type engagement between the torch head and the torch body by relative rotation, as disclosed in Japanese Examined Patent Publication No. Showa 63-13793 and Japanese Unexamined Utility Model Publication No. Heisei 3-14076.
A third conventional fixing means (3) is a quick joint system, in which a steel ball is engaged with a recessed portion, as disclosed in Japanese Examined Utility Model Publication No. Showa 5-19186 and Japanese Unexamined Patent Publication No. Heisei 6-198450.
In the processing torch, expendables, such as an electrode, a nozzle and so forth, are included. For reducing the burden of exchanging, and for shortening of exchanging time, a separable assembling type processing torch has been considered, whereby when the torch head is released from the torch base, a water passage is separated at the connecting portion to cause leakage of the water to make the connecting surface wet.
Upon separation of the torch head and the torch base, a water pump is stopped. The water may not flow in the connecting portion. Therefore, it is considered that leakage of water may not be caused. However, water remains in the path from the pump and the torch, and this remaining water may flow out from the connecting portion upon separation, to cause water leakage. Then, upon arc firing, electric leakage or insulation failure can be caused.
Therefore, in order to prevent the water leakage, it becomes necessary to have a water stop mechanism upon separation of the torch. The one disclosed in Japanese Unexamined Patent Publication No. Heisei 6-198450 and Japanese Unexamined Patent Publication No. Showa 62-275580, while a difference of water passage and gas passage is present, closes the passage upon separation, and upon assembling, the passage is opened by the projection.
The above prior art (1) is reliable as a secure fixing means, but the cap nut has to be rotated for several turns upon connection and separation, resulting in a long period for connection and separation. Certain measure may be taken by making the thread pitch of the cap nut greater to reduce rotation angle for threading. However, when the pitch is made greater, greater rotation torque becomes necessary to exert the same threading force. Therefore, it is not expedient to provide the greater pitch for significant load upon exchanging of the torch head. On the other hand, in case of the cap nut, it is easy to cause crushing of the thread. Thus, in consideration of automatic exchange by a machine, special measure has to be taken so as not to crush the thread.
In the above-mentioned prior art (2), the claw shaped projection is hooked to the projection with an inclination to generate an axial force by the inclination without using threading. In this system, sufficient tightening which can not be established or engagement which can be easily loosened results when an error occurs in the relative position of the projections in the axial direction. Therefore, in order to be certainly fixed, adjustment of both projections becomes necessary. Also, since a plurality of torch heads are connected as exchanged to one torch base, adjustment of the relative position of the projections becomes necessary for every torch head, resulting in a long period for performing an exchanging operation.
Furthermore, another problem of the foregoing prior art (2) is that, for the structure to establish slip contact between the projections with respect to each other, if the contact surface is worn, the relative position of the projections may diverge to make the axial biasing force smaller to require re-adjustment of the relative position between the projections. On the other hand, the gradient of the spiral projection is determined by an angle depending upon a required axial motion magnitude and rotatable angle. A 2 to 5 mm axial motion magnitude from abutment of an O-ring at the inserting portion should be required. When the engaging portions of respective projections are formed at two portions on the circumference, the rotation angle becomes 180.degree. and the gradient is determined based thereon. However, since the thus determined gradient is relatively large, a rather large rotational torque becomes necessary for obtaining sufficient axial force making it difficult to connect and separate manually.
Furthermore, in the above-mentioned prior art (3), connection can be completed by inserting the torch head into the torch base in the axial direction and thus is advantageous to be quite easily connected and disconnected. However, this holds a drawback because a small pushing force in the axial direction at the connecting portion to causes a play in the axial direction. Therefore, a complicated structure becomes necessary for generating a sufficient pressure in the axial direction to make the connecting portion large. In the construction disclosed in Japanese Examined Utility Model Publication No. Heisei 5-19186, axial depression force is generated by means of a spring. However, since the depression force becomes the force necessary upon insertion, when the spring force is set to permit manual loading, sufficient axial depression force cannot be obtained.
The reason why sufficient axial depression force is necessary at the connecting portion is that the torch head can be offset from the torch base due to vibration or so forth due to movement thereof to cause offset of the tip position of the torch to cause an adverse influence on cutting performance. Also, when an O-ring is present on the connecting surface, further depression force becomes necessary to make sealing effective. In the case where the connecting structure requires surface pressure for flowing sufficient plasma current, further axial depression force becomes necessary.
The seal surface of the inserting portion having the water passage and the gas passage of the torch base and the torch head in the processing torch, is generally straight. With respect to the O-ring provided at this portion, axial force becomes necessary from the beginning of insertion to make connection and disconnection difficult. The structure where the seal surface of the inserting portion is formed into a tapered shape has been disclosed in Japanese Examined Patent Publication No. Heisei 3-27309. In practice, an O-ring for sealing becomes necessary. At this time, in order to form coaxial passages, the inner diameter of the O-ring becomes large to make a total contact area of the O-ring large. Accordingly, a large axial force becomes necessary to crush the O-ring for establishing a seal On the other hand, concerning water leakage upon separation in the connecting portion of the water passage, this can be prevented by applying the opening and closing valve disclosed in Japanese Unexamined Patent Publication No. Heisei 6-198450 and Japanese Unexamined Patent Publication No. Showa 62-275580. In such construction, when the connecting portion is disconnected during operation of the pump, the valve is closed to build-up a dangerously high pressure within the piping (connecting portion) between the pump and the valve. Furthermore, an impulsive load may act on the pump to cause failure. On the other hand, in the case of the separable type torch as disclosed in Japanese Unexamined Patent Publication No. Heisei 6-198450, when a nozzle at the tip end, an electrode or so forth is to be exchanged in the condition where the connecting portion is connected, water leakage should be caused since the valve is held open.
In view of the problems set forth above, it is a first object of the present invention to provide a processing torch which can be easily be separated from and connected to a separably assembling type torch main body manually, which can effectively seal a connecting portion of a water passage or a gas passage in the torch main body, and which can prevent water leakage even upon exchanging of expendables or upon separation.
On the other hand, in the case of the conventional separable type torch, when the torch head is separated with respect to the torch base, the water passage is separated at the connecting portion. Therefore, a connecting portion of the water passage is provided with a water stop valve for preventing the water leakage which can automatically close the water passage in response to separation of the torch head.
In the particular structure disclosed in Japanese Unexamined Patent Publication No. Showa 60-9586, water stop valves for water passages of an in-flow side and an out-flow side are arranged at positions distanced in a direction perpendicular to an axis of the torch base. Respective water stop valves are opened by connection of the torch head and closed in response to separation.
On the other hand, in the case of this kind of separable type torch, a current to the electrode of the torch head flows to the electrode from the torch base to the torch head. At this time, the foregoing current may flow even to the water stop portion provided in the water passage, when these structural parts are electrically conductive bodies.
However, in the case of the water stop structure of the water passage as disclosed in Japanese Unexamined Patent Publication No. 60-9586, it becomes necessary to separately provide two water stop valves of the same structure, separately. Therefore, this prevents the connecting portion from being constructed in a compact manner, and requires a greater number of processing process making it difficult to lower the cost thereof.
On the other hand, the passages at the in-flow side and the out-flow side mutually communicated with via respective water stop valves are provided separately at the base end side of the torch head to make the processing at this portion troublesome.
Also, when the electrode current flows through the water stop valve in the water passage, particularly, when the current flows through the spring for stopping water biasing the valve body of the water stop valve in the closing direction, the spring for stopping water may be melted down since the current is a large current and the wire forming the spring for stopping water has a small diameter, thereby spoiling the water stop function.
In view of the problems set forth above, a second object of the present invention is to provide a processing torch which can simplify a construction of a water stop valve for preventing water leakage at the connecting portion in respective water passages for inflow and outflow, which permits the connecting portion to be compact, which permits significant reduction of the processing cost, which can prevent the electrode current from flowing through a spring for stopping water in respective water stop valves, and which and can prevent the spring from melting down.